The present invention concerns a friction clutch mechanism, notably for a motor vehicle, and relates more particularly to a clutch equipped with a device for compensating for the wear due notably to the wear on the friction lining or linings, this device, hereinafter referred to as a wear take-up device, operating gradually as the wear occurs on the lining or linings.
A conventional friction clutch generally has a reaction plate forming part of an engine flywheel, possibly in two parts in order to form a damping flywheel or a flexible flywheel, fixed with respect to rotation to a first shaft, usually a driven shaft such as the crankshaft of the internal combustion engine, and supporting through its external periphery a rear cover to which there is attached, with axial mobility, at least one front pressure plate.
The pressure plate is fixed with respect to rotation to the cover and reaction plate whilst being able to move axially under the action of axially acting engaging means controlled by disengaging means. The engaging means can consist of helical springs or two Belleville washers mounted in series, subjected to the action of disengaging levers forming the disengaging means.
Generally, the engaging and disengaging means form part of the same piece, for example a metallic diaphragm bearing on the cover. The diaphragm can be mounted in series or in parallel with a Belleville washer in order to provide assistance for the disengagement force.
A friction disk, carrying friction linings at its external periphery, fixed with respect to rotation to the shaft, usually a driven shaft such as the input shaft of the gearbox, is interposed between the pressure plate and the reaction plate so as to be clamped between them when the clutch is in the engagement position in order to transmit the torque from the driving shaft to the driven shaft.
Conventionally, the friction linings are mounted on an axially elastic support coupled rigidly or elastically to a hub fixed with respect to rotation to the driven shaft. By virtue of this arrangement the friction disc assists the diaphragm during the operation of disengaging the clutch. In a variant, the support is embedded at its external periphery in a friction lining.
Conventionally, the engaging means, cover and pressure plate form part of a unitary assembly referred to as a friction clutch mechanism.
The engaging means control the axial movement of the pressure plate when they are actuated by a clutch release bearing by means of the disengaging means.
The clutch release bearing can be controlled mechanically, hydraulically, electrically or electro-mechanically. The control can be of the manual, automatic or semi-automatic type.
During the service life of such a clutch, the friction lining or linings and the counter-materials, pressure plate and reaction plate wear, which cause a variation in the axial position of the pressure plate, that of the axially acting engaging means and that of the clutch release bearing, resulting in a variation in the axial clamping force between the friction disc on the one hand and the pressure and reaction plates on the other hand, because of the changes in the operating conditions of the engaging means, and the force necessary for disengaging is affected thereby. By providing such a clutch with a wear take-up device, these drawbacks are avoided, the engaging means, as well as the clutch release bearing, usually in constant abutment on the disengaging means, occupying the same position when the clutch is in the engagement position, which makes it possible to reduce the axial bulk of the friction clutch.
The French patent application FR-96.11297 filed on Sep. 17 1996 and published under the number 2 753 503 describes and depicts in FIGS. 21 to 26 a friction clutch mechanism, notably for a motor vehicle, of the type having a rear cover 52, a front pressure plate 51 connected with respect to rotation to the cover 52 while being able to move axially with respect to it, abutment means 14 carried by the pressure plate 51, axially acting engaging means 53 acting between the cover 52 and the support means 14, and a wear take-up device.
The wear take-up device comprises on the one hand means 54 with ramps 56 carrying a set of external teeth 59 and placed between the pressure plate 51 and the abutment means 14 in order to constitute a pressure plate 51, 54 with a variable thickness between its friction face and the abutment means 14 and comprises moreover a unit carried by the cover 52 and which includes a piece 62, secured to the cover 52, forming a support for fixing the unit to the cover 52.
The support 62 is roughly in a U-shape with a top central web 64, in the general form of a horizontal plate, oriented roughly tangentially, and two opposite lateral wings 65, 66, each of which extends vertically downwards in an axially oriented plane perpendicular to the top web and each of which has a hole 61 for rotatably mounting, with the interposing of bearings 3, an assembly 67, 63, 60, the piece 62 forming a support having a front fixing lug 68 which extends vertically upwards in a transverse plane perpendicular to the overall axis of the mechanism from a front transverse edge of the plate forming a central web 64 and which is fixed by riveting to a peripheral edge of the cover 52.
The assembly has notably a shaft carrying a worm, a ratchet wheel and a helical spring. The support also carries an elastic member provided on the one hand with a control tongue on the other hand with a non-return catch.
The control tongue is able to be manoeuvred by an actuator forming part of the engaging means of the clutch and cooperates, as does the catch, with the teeth on the ratchet wheel.
The worm cooperates with the teeth on a set of teeth belonging to the ramp means produced in the form of a ring with ramps disposed axially between the support means of the engaging means and the pressure plate. The worm cooperates with this set of teeth and with means of guiding in rotation, comprising the helical spring, which are made operational by the wear on the friction lining when the clutch is engaged. The worm is mounted tangentially with respect to its associated set of teeth.
It is desirable to facilitate the assembly of the components of the unit and notably to allow the inclination or not of the shaft by offsetting the holes of the wings which receive the opposite ends of the shaft.
For this purpose, the invention proposes a clutch mechanism of the type mentioned above, characterised in that at least one of the lateral wings of the support carries a bearing with a hole at the centre which receives one end of the shaft and which is housed in a blind hole in the wing in which it is slipped and then trapped, notably by crimping. By virtue of the invention, it is possible to form an assembly consisting of worm, ratchet wheel and shaft which is mounted easily in the support.
According to other characteristics of the invention:
each of the two lateral wings carries a bearing;
the holes are offset axially with respect to each other in order to incline the worm and shaft;
the central holes in the bearings are inclined in order to incline the worm and shaft;
the support carries an elastic member provided with a control tongue carried by a return on the said elastic member and a non-return catch; the non-return catch and control tongue cooperating with a ratchet wheel fixed to the worm and the return on the elastic member having two portions of different heights disposed on each side of the control tongue;
the bearings are engaged in blind holes produced in the wings and locked by crimping in the said holes.
In the above, locking by crimping, resulting in a flow of material, is a means for partially closing off the end of the blind hole and preventing the bearing from coming out. This partial closure can be effected by welding or bonding.
Naturally, other locking means can be used, for example by attaching a supplementary piece to the support at the open end of the blind hole.
This piece, after it is fixed to the support, cooperates with the bearing in order to immobilise the latter, for example by cooperation of shapes.
The supplementary piece is for example fixed by bonding, welding, force-fitting or crimping to the wings.
Naturally, all combinations are possible. Thus, one of the bearings can be trapped and locked by at least one supplementary piece or by welding or bonding. Only one of the wings may be provided with a blind hole.
It is then necessary, for example, to introduce the shaft on a slope with the bearing concerned in the closed hole, and then to cause the assembly to pivot in order to introduce the other bearing into the blind hole and finally to trap the assembly.
As a variant, at least one of the blind holes can open out in another edge of the wing.